The invention relates to a procedure for hardening the bearing surfaces of a shaft or axle, in particular a crankshaft or camshaft. In addition, the invention relates to a device for hardening the bearing surfaces of shafts or axles that rotate around their longitudinal axis during hardening, in particular of crankshafts and camshafts.
In particular when hardening the bearing surfaces of crankshafts, the problem is that the crankshaft becomes distorted due to the respective locally limited exposure to heat. This distortion becomes particularly evident when hardening a main bearing of the crankshaft.
DE 31 37 398 C1 proposed a procedure and a device of the aforementioned kind, which enable a hardening of crankshafts with a minimal distortion. In this prior art, the distortion that arises during inductive heating of the respective bearing surface is ascertained. To this end, a measuring device is provided, which monitors the lift of the inductor carried on a pendulum bearing that abuts the bearing surface. If the lift is delayed, the heat output of the inductor is increased. By contrast, if a reduction in lift is detected, the heat output is also reduced. At the same time, the crankshaft is clamped on either side of the bearing to be hardened in a collar plate. These support surfaces encompass three rollers sitting on the crankshaft in regular angular intervals, via which the respective support force is exerted on the crankshaft. As a result of the interaction between the support forces exerted by the collar plates and variable heat output, the distortion of the crankshaft that accompanies the hardening is kept to a minimum.
It has been found in practice that, in particular when the surfaces of the lifting and main bearing of a crankshaft are hardened in sequence, the minimization of distortion achieved with the known procedures or known device is insufficient to satisfy the increased requirements placed on the dimensional stability of shafts hardened in this way.
Proceeding from these problems, the object of the invention is to develop a procedure and a device of the kind described above in which the distortion of a shaft or axle that arises as the bearing surfaces are hardened is further reduced.
On the one hand, this object is achieved with a procedure for hardening the bearing surfaces of a shaft or axle, in particular a crankshaft or camshaft, in which the bearing surfaces to be hardened are hardened sequentially with the shaft or axle turning around their longitudinal axis by means of a heating or quenching device, in which the distortion of the shaft or axle that arises in the area of the respective bearing surface during the course of hardening is determined, in which the shaft or axle is supported by at least one supporting device during hardening, which is placed against a previously hardened bearing surface, and in which the position of the supporting device is regulated taking into account the distortion determined for the bearing surface, against which the supporting device is placed.
On the other hand, the above object is achieved by a device for hardening the bearing surfaces of shafts or axles that rotate around their longitudinal axis during hardening, in particular of crankshafts or camshafts, which is equipped with a heating and quenching device, a supporting device for supporting the shaft or axle during hardening of the bearing surfaces, and with a device for determining the distortion of the respective shaft or axle, wherein a controller with a memory for storing the result of determining the distortion is present, and the supporting device encompasses a setting device linked with the controller, which changes the setting of the supporting device taking into account the stored measured values.
The invention is based on the idea that the distortion that arises when hardening a bearing surface is also taken into account if a supporting device is placed against the respective bearing point to support the shaft or axle while hardening the next bearing surface to be machined. As a result, the setting device is guided as a function of the distortion of the shaft or axle respectively present in the area of the supporting point. In this way, the supporting forces applied by the supporting device can be adjusted to the actual circumstances.
One the one hand, this makes it possible to adjust the supporting forces acting on the shaft or axle in such a way as to avoid undesired additional deformations of the shaft or axle. These deformations can also be caused by motions of the supporting devices that have not been adjusted to the actual circumstances. On the other hand, supporting forces can be exerted on the shaft or axle in a targeted fashion by appropriately controlling the setting of the supporting device, in order to achieve a deformation of the shaft or axle suitable for counterbalancing the distortion.
In this case, the setting of the supporting device is regulated as a function of the rotational setting of the shaft or axle that rotates around its longitudinal axis during the hardening process. In this way, the invention makes it possible to control the support of the machined shaft or axle as a function of rotational angle, while at the same time balancing out those deformations that set in due to the preceding hardenings initiated at another point. By taking into account the deformations that arise during the hardening of the bearing surfaces of a shaft or axle as specified by the invention, distortion of the shaft or axle is minimized after all bearing surfaces have been hardened.
The respective distortion of the individual bearing points taken into account while adjusting the setting of the supporting device can be determined by ascertaining the respective distortion that arises while hardening the bearing surfaces using a pattern shaft or pattern axle, and, while hardening the subsequently machined shafts or axles, regulating the setting of the supporting device placed against a bearing surface of the machined shafts or axles respectively hardened beforehand, taking into account the distortion determined using the pattern shaft for the respectively corresponding bearing surface. In this embodiment of the invention, it is assumed that the same distortion always arises when hardening the bearing points of shafts or axles in a large series of work pieces with identical geometry. For this reason, the distortion that arises when hardening each bearing point is determined using a pattern. Once determined in this way, the distortion is taken into account when regulating the setting of the supporting device during the hardening of all subsequently machined shafts or axles in the same series. The cost for determining distortion can be minimized in this way.
The accuracy with which the arising distortion is counterbalanced can be improved by determining the respective distortion that arises while hardening a bearing surface (H1), by placing the supporting device against the hardened bearing surface after the bearing surface has been hardened in order to support the shaft or axle while hardening the next bearing surface, and by regulating the setting of the supporting device taking into account the distortion determined for the hardened bearing point. In this embodiment of the invention, the respective distortion that actually arises on the individual bearing surfaces is determined for each shaft or axle. This distortion is then taken into account when supporting the shaft or axle while hardening the bearing surface machined next. In this way, all deformations of the shaft or axle that accompany the hardening process are directly counterbalanced, taking into account the actual circumstances existing for each individual work piece.
Regardless of how the distortion is determined, the distortion should be ascertained with respect to its magnitude and relative position, so that the supporting forces applied by the supporting device can be easily controlled depending on the rotational angle according to the invention.
Basically, the distortion can be determined manually after each hardening step using suitable measuring devices. However, it is favorable for automated operation that this distortion of the machined shaft or axle be automatically determined.
One embodiment of the invention that is inexpensive to manufacture and advantageous in terms of space is characterized in that the measuring device is coupled with the heating and quenching device, and a change in the path traversed by the heating or quenching device during a rotation of the shaft or axle is determined as a gauge for the distortion of the shaft or axle. Of course, separate measuring devices independent of the heating and quenching device can also be used, e.g., optical, electrical or other measuring systems, which are suitable for determining the change in a geometric shape or position.
The invention can be used in a particularly advantageous manner in conjunction with those devices in which the heating and quenching device encompasses an inductive heating unit. Precisely these kinds of inductive heating units make it possible to influence the respectively machined work piece with heat.
It is advantageous if the setting device can be moved in at least two degrees of freedom. This makes it possible to compensate for each deformation of the shaft or axle with an appropriate setting of the setting device. In this case, the adjustability of the setting device can be easily realized by virtue of the fact that the setting device encompasses a hydraulically, pneumatically or electrically activatable power-generating device. If this power-generating device encompasses a cylinder, it is beneficial with respect to reducing the space required for an extension of the piston of the cylinder to form a support on which the shaft or axle is supported. A supporting device of this design exhibits a compact structure that can easily be assembled even in more cramped areas.
To enable such a reliable support for the shaft or axle that rotates around its longitudinal axis during the hardening process, the supporting device should exhibit a roller seating for the shaft or axle, wherein the roller seating preferably exhibits two rollers, whose rotational axes are situated in a shared plane. These rollers form a two-point bearing, on which the respective bearing surface is reliably supported when the distance between the rollers is less than the diameter of the shaft or axle in the area of the bearing surface against which the supporting device rests. In this connection, it is also advantageous if a third roller is provided, acting on the bearing surface at a distance from the other two rollers. In this way, the supporting point can be gripped by the rollers of the supporting device, thereby ensuring a support that encompasses the entire periphery of the respective supporting point.
The latter makes sense in particular when the supporting forces are intended to apply an additional supporting force on the shaft or axle that balances out the existing distortion of the shaft or axle. A configuration of the device according to the invention that is particularly suitable for this purpose is characterized in that at least one of the rollers is hinged and coupled with a setting device, by means of which the hinged roller can be pivoted in its support setting. A supporting device designed in this way can apply both negatively and positively directed supporting forces relative to the desired deformation of the shaft or axle.